The invention relates to poly-o-hydroxyamide, polybenzoxazole, and electronic component including a dielectric, all having a barrier effect against copper diffusion. In addition, the invention relates to processes for preparing poly-o-hydroxyamides, polybenzoxazoles, and electronic components.
In order to avoid an inductive disturbance of signals that is caused by capacitive coupling, conductor tracks adjacent one another in microchips are insulated from one another by a dielectric disposed between the conductor tracks. Compounds that are to be used as a dielectric must meet various requirements. Thus, the signal transit time in microchips depends both on the material of the conductor track and on the dielectric that is disposed between the conductor tracks. The lower the dielectric constant of the dielectric, the shorter, too, is the signal transit time. The silica-based dielectrics used to date have a dielectric constant of about four (4).
These materials are gradually being replaced by organic dielectrics that have a substantially lower dielectric constant. The dielectric constant of these materials is generally below three (3).
In the microchips customary at present, the conductor tracks preferably include aluminum, AlCu, or AlCuSi. With increasing integration density of the memory chips, there is a changeover to copper as conductor track material, owing to its lower electrical resistance compared to aluminum. Copper permits shorter signal transit times and hence a reduction in the conductor track cross section. In contrast to the techniques customary to date, in which the dielectric is filled in the trenches between the conductor tracks, in the copper damascene technique, the dielectric is first structured. The resulting trenches are first filled with copper and then excess copper is mechanically ground away. The dielectric must therefore be stable to the materials used for grinding and must have sufficient adhesion to the substrate in order to avoid becoming detached during the mechanical grinding process. Furthermore, the dielectrics must also have sufficient stability in the subsequent process steps in which further components of the microchips are produced. For this purpose, they must have, for example, sufficient thermal stability and must not undergo decomposition even at temperatures of more than 400xc2x0 C. Moreover, the dielectrics must be stable to process chemicals, such as solvents, strippers, bases, acids or aggressive gases. Further requirements are good solubility and a sufficient shelf life of the precursors from which the dielectrics are produced.
In order to be suitable as a dielectric for microchips, it is very important that the metal of the conductor tracks does not diffuse into the dielectric even at elevated temperature. The production of microchips includes the production stages that cause a thermal load reaching 400xc2x0 C. or higher, such as, for example, oxide deposition, copper annealing, or tungsten deposition from the gas phase. In order to avoid diffusion of the metal into the dielectric, a barrier is provided between dielectric and metal. Such barriers include, for example, titanium nitride, silicon nitride, silicon carbide, or tantalum nitride. The barrier acts neither as a good dielectric nor as a good conductor. However, it requires space since a certain layer thickness of the barrier is required in order effectively to suppress diffusion of the metal into the dielectric. With increasing integration density, i.e. decreasing width of the conductor tracks, the proportion of space that is occupied by the barrier increases substantially relative to the width of the conductor track. In the case of a conductor track width of 100 nm or less, the barrier may optionally occupy up to 10% of the available width. Therefore, further miniaturization of the semiconductor components is made more difficult. For further miniaturization of the microchips, the width of the barrier must therefore be further reduced or, most preferably, the barrier should be completely dispensed with.
Polybenzoxazoles (PBOs) are polymers that have very high heat resistance. The substances are already used for the production of protective and insulating layers in microchips. Polybenzoxazoles can be prepared by cyclization of poly-o-hydroxyamides. The poly-o-hydroxyamides have good solubility in organic solvents and good film formation properties. They can be applied to electronic components in a simple manner by the spin-coating technique. In a thermal treatment in which the poly-o-hydroxyamide is cyclized to give the polybenzoxazole, a polymer that has the desired properties is obtained. Polybenzoxazoles can also be processed directly in their cyclized form. In this case, however, there are as a rule difficulties with the solubility of the polymer. Building blocks for poly-o-hydroxyamides are described, for example, in DE 100 11 608, which corresponds to U.S. Pat. No. 6,531,632.
Further insulation materials stable at high temperatures are disclosed, for example, in International PCT Publication Nos. WO 97/10193, WO 91/09081, and WO 91/09087 and European Patent Nos. EP 23 662 and EP 264 678. In the case of these materials, however, a barrier must be provided between conductor track and dielectric in order to avoid diffusion of the metal into the dielectric at high temperatures.
It is accordingly an object of the invention to provide a poly-o-hydroxyamide, a polybenzoxazole, and an electronic component including a dielectric having a barrier effect against copper diffusion, and processes for preparing poly-o-hydroxyamides, polybenzoxazoles, and electronic components that overcome the hereinafore-mentioned disadvantages of the heretofore-known devices of this general type and that involve a polymer that is stable at high temperatures for use in microchips. The polymer permits the production of finer conductor tracks in microchips.
With the foregoing and other objects in view, there is provided, in accordance with the invention, a poly-o-hydroxyamide of the formula I 
in which:
Y2 is 
Y1 and Y3, in each case independently of one another, and are selected from 
Z1, Z2 and Z3, in each case independently, are 
A, if a=0 and/or d=1, is 
and A, if a=1 and/or d=0, is 
R2 is xe2x80x94H, xe2x80x94CF3, xe2x80x94OH, xe2x80x94SH, xe2x80x94COOH, xe2x80x94N(R5)2, an alkyl group, an aryl group, a heteroaryl group, and 
R5 is an alkyl, an aryl or a heteroaryl radical;
a is 0 or 1;
b is 1-200;
c is 0-200;
d is 0 or 1;
e is 0-10;
f is 0-10;
g is 0-10;
h is 1-10;
n is 0 or 1; and
x is 0-10 if R3 is xe2x80x94CH2xe2x80x94.
The poly-o-hydroxyamides of the formula I dissolve in many organic solvents, such as, for example, acetone, cyclohexanone, diethylene glycol mono- or diethyl ether, N-methylpyrrolidone, xcex3-butyrolactone, ethyl lactate, methoxypropyl acetate, tetrahydrofuran, or ethyl acetate.
They can be applied to a substrate very readily in a uniform film by spin-coating, spraying, or dipping techniques. The evaporation of the solvent gives a homogeneous film that has a uniform layer thickness and complete fills even trenches and contact holes with a high aspect ratio. The poly-o-hydroxyamides of the formula I can be cyclized by heating to give the corresponding polybenzoxazoles; no bubble formation or cracking is observed. Even at high process temperatures of 400xc2x0 C. or higher, no, or at least only very little, diffusion of metal from the conductor tracks into adjacent regions of the dielectric is observed. The barrier usually disposed between conductor track and dielectric can therefore either be made very thin or even completely dispensed with.
The repeating units characterized in the formula I by the indices b and c can, if c is  greater than 0, be randomly distributed in the polymer strand. However, it is also possible to prepare the poly-o-hydroxyamide of the formula I by block copolymerization so that segments of the polymer are composed in each case only of one of the repeating units denoted by the indices b and c. The chain length of the poly-o-hydroxyamides of the formula I can be controlled by the stoichiometric ratios of the starting materials and the reaction conditions, for example the reaction temperature, dilution or rate of addition of the individual components. However, the polymer does of course have a molecular weight distribution, i.e. in each case, mixtures of polymers having a different molecular weight and hence different values for the indices a, b, c, and d may be present. In the preparation of poly-o-hydroxyamides of the formula I, the reaction is preferably carried out in such a way that a narrow molecular weight distribution is achieved. The maximum of the molecular weight distribution is established so that it lies within the ranges characterized by the indices a to d. Within the molecular weight distribution, preferably at least 90% of the polymers are within the limits specified by the indices a to d. The molecular weight of the poly-o-hydroxyamides of the formula I can be determined by customary methods, for example gel permeation chromatography.
The substitution pattern of the groups Z1, Z2, and Z3 is chosen so that in each case a pair formed from an xe2x80x94NH group and an OR1 group are disposed in the ortho position to one another. This is necessary in order to permit cyclization to an oxazole ring in the cyclization of the poly-o-hydroxyamides of the formula I. The poly-o-hydroxyamides of the formula I may carry a terminal group A that, after the polymerization, is introduced into the polymer as a terminal group via a corresponding activated compound. Suitable compounds are, for example, acid chlorides, alkyl halides, or alcohols. The precursor required for introduction of the terminal group A is chosen according to the group that the polymer carries as a terminal group after the polymerization. If the index a=0 or the index d=1, the terminal group A is bonded to an NH group. A suitable activated precursor is then, for example, an acid chloride. If the index a=1 or the index d=0, the terminal group A is bonded to a CO group. Suitable reagents for introducing the terminal group A are then, for example, halides, alcohols, or amines.
If the group R2 is an alkyl group, this preferably includes 1 to 10 carbon atoms. The alkyl group may be linear or branched. Suitable groups are, for example, a methyl group, an ethyl group, a propyl group, or an isopropyl group. If R2 is an aryl group, this preferably includes 6 to 20 carbon atoms, it also is possible for the aromatic system to be substituted by alkyl groups. Examples of suitable groups are the phenyl group, the methylphenyl group or the naphthyl group. If R2 is a heteroaryl group, this preferably includes 4 to 20 carbon atoms and 1 to 4 heteroatoms. Suitable heteroatoms are, for example, nitrogen, oxygen, or sulfur.
If R5 is an alkyl group, this may be linear or branched and preferably includes 1 to 10 carbon atoms. If R5 is an aryl group, this preferably includes 6 to 20 carbon atoms, the aromatic system preferably being formed by 6-membered rings. If R5 is a heteroaryl group, this preferably includes 4 to 10 carbon atoms and 1 to 4 heteroatoms. Here too, suitable heteroatoms are nitrogen, oxygen, or sulfur.
The film quality of the film produced with the poly-o-hydroxyamide of the formula I is influenced, inter alia, by the chain length of the polymer. Particularly preferably, the poly-o-hydroxyamide of the formula I has a composition such that the index b assumes values between 5 and 50 and the index c values between 0 and 50. In a particular embodiment, the index c assumes values in the range from 1 to 50. In a preferred embodiment, the poly-o-hydroxyamide of the formula I includes ether bridges. In this case, the index n in the structural element Y2 assumes the value 2.
The polybenzoxazoles produced from the poly-o-hydroxyamide of the formula I have a dielectric constant of less than 3. If the dielectric constant is to be even further reduced, pores are provided in the polybenzoxazole. For this purpose, the poly-o-hydroxyamide of the formula I may include further repeating units that are thermally labile and liberate a gas with decomposition on heating. The gas can diffuse out of the polybenzoxazole so that a cavity is formed in the polybenzoxazole.
The thermally labile repeating unit is preferably provided as a block in the poly-o-hydroxyamide. This can be achieved, for example, by first preparing oligomers from the thermally labile repeating units and then reacting these with the poly-o-hydroxyamide of the formula I. However, it is also possible first to prepare a poly-o-hydroxyamide of the formula I by polymerization and then to graft the thermally labile repeating units onto the poly-o-hydroxyamide in a further polymerization reaction. The decomposition temperature of the thermally labile repeating units should be chosen so that it is below the glass transition temperature of the poly-o-hydroxyamide of the formula I. Suitable repeating units by which the poly-o-hydroxyamide of the formula I can be supplemented in order to obtain a thermally labile copolymer are derived, for example, from polypropylene oxide, polymethyl methacrylate, and aliphatic polycarbonates, such as, for example, polypropylene carbonate and polyethylene carbonate. In addition to the thermally labile repeating units, other repeating units may also be used if they eliminate a gaseous product on heating. The proportion of the thermally labile repeating units in the copolymer is preferably chosen to be between 5 and 60% by weight of the copolymer. Such copolymers are described, for example, in U.S. Pat. No. 5,776,990 to Hedrick et al.
Pore formation can also be achieved by adding to the poly-o-hydroxyamide of the formula I a suitable porogen that decomposes on heating, gaseous products being liberated. Suitable porogens are, for example, citric acid, malic acid, or malonic acid.
As already mentioned, the polybenzoxazoles obtained from the poly-o-hydroxyamides of the formula I by cyclization have advantageous properties. The adhesion of the polybenzoxazole prepared from the poly-o-hydroxyamide of the formula I to surfaces relevant for microchip technology, such as silicon, silicon carbide, silicon carbonitride, silicon nitride, silica, titanium, tantalum, titanium nitride, tantalum nitride or silicon oxynitride, is very good. Furthermore, the polybenzoxazoles have high resistance to chemicals as used in the production of microchips, such as solvents, strippers, bases, acids or aggressive gases. The polymer materials are therefore very suitable for microelectronic applications. In addition, the materials are also outstandingly suitable for the copper damascene technique. During the copper grinding process, no disadvantageous effects occur, such as delamination, cracking or bubble formation. The polybenzoxazoles according to the invention surprisingly inhibit the diffusion in the dielectric. In addition to the electrical insulation function, they can therefore also be used as a diffusion barrier for copper. It is therefore possible to dispense with a barrier between dielectric and conductor track, or the barrier can be made substantially thinner. As a result of the smaller amount of space required, this permits an increase in the integration density. If the barrier can be completely dispensed with, the use of the polybenzoxazoles according to the invention furthermore results in a reduction in the production costs of the microchips since the step for the production of the barrier is omitted.
The poly-o-hydroxyamides of the formula I are prepared from bis-o-aminophenols and dicarboxylic acids or their derivatives. The invention therefore also relates to a process for the preparation of poly-o-hydroxyamides of the formula I, at least one monomer of the formula II 
in which Z is Z1, Z2, or Z3, and Z1, Z2, Z3, and R1 have the abovementioned meaning,
being reacted with at least one dicarboxylic acid or one activated dicarboxylic acid derivative of the formula III 
xe2x80x83in which L is a hydroxyl group or an activating group and Y is Y1, Y2, or Y3, and Y1, Y2, and Y3 have the abovementioned meaning.
For example, acid chlorides or activated esters, for example sulfonic esters, can be used as an activating group for the dicarboxylic acid derivatives of the formula III. The reaction of the monomers of the formula II and the dicarboxylic acids of the formula III can, however, also be effected in the presence of a compound which activates the dicarboxylic acid, such as, for example, carbonyldiimidazole or dicyclohexyl-carbodiimide. In principle, all reagents that bind the water formed in the reaction to themselves are suitable. For the preparation of the poly-o-hydroxyamides of the formula I, the monomers of the formula II and dicarboxylic acids or optionally the dicarboxylic acid derivatives of the formula III are reacted in an organic solvent at from xe2x88x9220 to 150xc2x0 C. in the course of from 5 to 20 hours. If required, terminal groups of the polymer can be blocked by a suitable reagent in order thus to introduce the terminal groups A. Suitable reagents have already been described in the explanation of the compound of the formula I. The poly-o-hydroxyamide of the formula I that is formed after the reaction is precipitated by dropwise addition of the reaction solution to a precipitating agent, washed and dried. Suitable precipitating agents are water and alcohols, such as isopropanol, butanol, or ethanol. Mixtures of these precipitating agents may also be used. The precipitating agent may suitably also contain from 0.1% to 10% of ammonia. After filtration and drying, the precipitated polymer can be directly further processed and, for example, dissolved in one of the solvents mentioned further above, for application to a semiconductor substrate.
The polymerization to give poly-o-hydroxyamide of the formula I can be carried out in the presence of a base in order to trap liberated acid. Suitable basic acid acceptors are, for example, pyridine, triethylamine, diazabicyclooctane, or polyvinylpyridine. However, it is also possible to use other basic acid acceptors. Compounds that are readily soluble in the solvent used for the synthesis, such as, for example, N-methylpyrrolidone, and in the precipitating agent, for example water or water/alcohol mixtures, or those that are completely insoluble in the solvent, such as, for example, crosslinked polyvinylpyridine, are particularly preferred. The acid acceptors can then be readily separated from the resulting poly-o-hydroxyamide of the formula I during the working-up of the reaction product.
Particularly suitable solvents for the polymer synthesis are xcex3-butyrolactone, tetrahydrofuran, N-methylpyrrolidone, and dimethylacetamide. However, any solvent in which the starting components are readily soluble can in principle be used.
In accordance with a further object of the invention, the invention relates to a process for the preparation of the polybenzoxazoles described, poly-o-hydroxyamides of the formula I being heated. Heating results in the formation of an oxazole ring with elimination of a small molecule, in general water, the polybenzoxazoles according to the invention being obtained. The mechanism taking place during the cyclization of the poly-o-hydroxyamides of the formula I to polybenzoxazoles is shown schematically below: 
On heating, the o-hydroxyamide undergoes cyclization to give the oxazole with water being liberated.
The polybenzoxazole prepared by the process according to the invention has a low dielectric constant of kxe2x89xa63.0 and adheres very well to the surfaces relevant for chip technology, such as silicon, silicon carbide, silicon carbonitride, silicon nitride, silica, titanium, tantalum, titanium nitride, tantalum nitride, or silicon oxynitride.
The invention therefore also relates to an electronic component that contains the polybenzoxazole described above. The polybenzoxazole can be disposed, for example, as a dielectric between conductor tracks or conductor track planes or as a buffer layer between microchip and a housing surrounding this.
The dielectrics according to the invention are outstandingly suitable for the copper damascene technique. During the grinding process, no disadvantageous effects occur, such as delamination, cracking or bubble formation.
Therefore, the invention also relates to a process for the production of an electronic component. A solution of the poly-o-hydroxyamide of the formula I in a solvent is first prepared. The solution is applied to a substrate and the solvent is evaporated so that a film is obtained. The film is then heated in order to cyclize the poly-o-hydroxyamide and to convert it into the polybenzoxazole of the formula III. The film is then structured in order to obtain a resist structure which has trenches and/or contact holes. A conductive material, for example copper, is then deposited on the resist structure so that trenches and/or contact holes are filled with the conductive material. Finally, excess conductive material is removed, for example by chemical mechanical planarization (CMP).
For example, lithographic methods can be used for structuring the polybenzoxazole film, an etch-resistant mask being produced on the film. The structure of the mask is then transferred to the film from the polybenzoxazole according to the invention by etching. The conductive material used is preferably copper. A barrier can be provided between dielectric and conductive material. For example, the materials already mentioned further above are suitable as material for the barrier. The microchip is then completed in a customary manner.
Furthermore, the invention relates to a process for the production of an electronic component. First, a solution of a poly-o-hydroxyamide of the formula I described above in a solvent first is prepared. The solution is then applied to a substrate that already has on its surface metallic structures between which trenches are formed. Such structures are, for example, conductor tracks. The solvent is evaporated so that the trenches are filled with the poly-o-hydroxyamide of the formula I. Lastly, the substrate is heated in order to cyclize the poly-o-hydroxyamide of the formula I to the polybenzoxazole. The microchip is then completed in a customary manner.
The adhesion of the poly-o-hydroxyamides of the formula I to surfaces relevant in microelectronics, such as, for example, silicon, silica, silicon nitride, tantalum nitride, glass or quartz, can be improved by adding adhesion promoters.
Other features that are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a poly-o-hydroxyamide, a polybenzoxazole, and an electronic component including a dielectric having a barrier effect against copper diffusion, and processes for preparing poly-o-hydroxyamides, polybenzoxazoles, and electronic components, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.